Identification of an estrogen receptor in the testis of the sea lamprey, Petromyzon marinus.

Employing a hydroxylapatite batch assay, estrogen-binding activities (EBAs) were demonstrated in the cytosol and nuclear extract of the testis of the anadromous sea lamprey, Petromyzon marinus. The lamprey testicular EBAs are sensitive to trypsin digestion and bind [3H]estradiol-17 beta with high affinities (cytosolic Kd = 0.52 nM; nuclear Kd = 0.39 nM) and limited capacities (cytosolic: 56.2 fmol/g tissue; nuclear: 68.2 fmol/g tissue). Androgens, progesterone, and corticosterone displayed little affinities for lamprey EBAs. Thus, lamprey testicular EBA possessed many definitive properties of an estrogen receptor as described in amphibian, reptilian, and mammalian studies. No specific binding to androgens was detected in either testicular subcellular fraction. The presence of a putative estrogen receptor in lamprey testis suggests a functional role of estrogen in testicular regulation in this ancient vertebrate.